Alpha-actinin-3 R577X Genotype is Associated with Muscle Power in Middle-aged Men and Women

Abstract

The alpha-actinin-3 (ACTN3) gene encodes a protein of the Z disk of fast-contracting myofibers, and a polymorphism of ACTN3 (C to T) results in complete loss of the protein. The ACTN3 genotype (R577X) has been found to be associated with performance in Australian elite athletes and responses to training, however, little is known about the importance of this polymorphism in the interindividual variation of strength and power in the general population. PURPOSE: To study the association of the R577X ACTN3 genotype with muscle strength and power in middle age. It was hypothesized that X allele carriers showed lower explosive and maximal strength. METHODS: The R577X ACTN3 polymorphism (rs1815739, Sequenom MassARRAY SNP) was typed in 151 males (47 +/− 0.67 yr) and 135 females (40.50 +/− 1.1 yr) of the Leuven Longitudinal Study on Fitness, Lifestyle and Health. Three commonly used strength and power tests were administered (HGR= hand grip, VTJ= vertical jump, SBJ= standing broad jump). Genotype-phenotype effects were tested using AN(C)OVA with body mass as covariate. RESULTS: Lack of ACTN3 (X/X carriers) was observed in 26% of males and 23% of females (X frequencies 0.49 in males, 0.45 in females, no violation of HWE). No association was found with HGR strength. For VTJ, corrected for body mass, XX genotype carriers perform consistently and significantly (P<0.01) lower than X/R or R/R genotypes. Having at least one copy of the ACTN3 coding allele (R/X andR/R genotypes) did not differentiate performance in females, however in males an additive effect of the R allele was present. Similar results were found for absolute VTJ performances. For SBJ performance, similar trends (n.s.) were found. The ACTN3 R577X genotype explained between 2.5 and 6% of total variance in VTJ performance. CONCLUSIONS: Also in the general adult population, individuals lacking the ACTN3 protein, show decreased power performance, however, no effects are found on isometric strength.